Dealkylation of alkyl aromatic compounds



Aug. 31, i965 TARo MUKAI ETAL DEALKYLATION OF ALKYL AROMATIG COMPOUNDS Filed Nov. l2

mmxm. ok SESS James E Gant! /`/V I/E/V TORS= Taro Muka/ A T TURA/EVS sv wm United States Patent O 3,204,007 DEALKYLATION F ARGMAI'IC ICtlll/iPt'J'tiD'S Taro Muira, Des Plaines, and .lames E. Gantt, Elmwood Park, El., assignors to Universal Oil Products Company,

'Des Plaines, Ill., a corporation ot Delaware Filed Nov. '12, 1963, Ser. No. 324,167 9 Claims. (Cl. 1260-672) This application is a continuation-in-part of our c0- pending application, Serial No. 103,633 led April 17, 1961, now abandoned.

This invention relates to a process for the dcalkylation of alkyl aromatic compounds. More particularly the invention is concerned with improvements in a process for dealkylating alkyl aromatic hyrdocarbons utilizing a catalytic composition of matter, said process being effected in the presence of an excess of hydrogen.

In recent years the necessity or need for a high grade, pure benzene has increased an appreciable amount. For example, benzene having a high technical grade purity is an important starting material for the production of alkyl aromatic sulfonates which are useful as detergents and surface active agents. These alkyl aromatic Suffonates are prepared by alkylating benzene with a long chain polymer containing from about 12 to about 15 carbon atoms or more in the chain, said polymer having been generally prepared by polymerizing propylene or butene. After the benzene has been alkylated the resultant compound may be sulfonated by any method Well known in the art to produce the corresponding sulfonic acids. These acids may then be neutralized by any basic material such as sodium hydroxide, potassium hydroxide, etc., to form the corresponding sulfonates such as the sodium or potassium salt of the alkyl aryl sulfonic acid. In addition to the aforementioned use of a relatively pure aromatic hydrocarbon, such as benzene, and also in some instances naphthalene, as intermediates in the preparation of detergents, the high grade, relatively pure aromatic hydrocarbons may also find uses as intermediates in the preparation of many organic compounds such as insecticides, pharmaceuticals, resins, dyes, perfumes, etc. While it is admitted that alkyl aromatic compounds such as toluene, ortho-xylene, meta-xylene, para-xylene, ethyl benzene, methyl naphthalene, dimethyl naphthalene, etc., may also be useful in the preparation of chemical compounds this invention is concerned mainly with the production of unsubstituted aromatic hydrocarbons. The feed stocks for the process of this invention may be obtained from many sources, for example, the by-products resulting from the processes utilized in the petroleum industry may contain aromatic hydrocarbons containing one or more alkyl substituents on the ring. Another source of feed stock for the process of this invention is the coal tar industry which finds that after distillation of coal the coal tar crudes contain a mixture of benzene, toluene, xylenes, naphthalene, etc. After the coal tar is refined and the hydrocarbons present are separated,

from each other by fractional distillation the toluene and xylenes which are recovered may then be dealkylated according to the process of the present invention to provide a greater yield of the desired product which, in this instance, comprises benzene.

According to the present process, the dealkylation of the alkyl substituted aromatic compounds is effected in the presence of an excess of hydrogen and a catalytic composition of matter, more fully described hereinafter, at elevated temperatures and pressures. When utilizing toluene and the xylenes or methylnaphthalene as the charge stock the principal reaction is, of course, demethylation of the aromatic ring to form benzene or naphthalene 3,204,007 Patented Aug. 3l, 1965 lCe plus methane. This reaction is strongly exothermic, the rate of the demethylation increasing slowly with an increase in temperature. However, the temperature must of necessity, be controlled within a desired range in order to remove the large amount of reaction heat which might build up and have a tendency to destroy the de sired product by hydrocracking the benzene, toluene, xylene or naphthalene to form carbon.

It is therefore an object of this invention to provide a process for the production of dealkylated aromatic hydrocarbons.

A further object of this invention is to provide a process whereby alkyl substituted aromatic compounds are dealkylated in the presence of hydrogen and a dealkylation catalyst in such a manner that the temperature of the reaction is closely controlled.

Taken in its broadest aspect, one embodiment of this invention resides in a process for the catalytic hydrodealkylation of an alkyl aromatic hydrocarbon which comprises passing said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at hydrodealkylating conditions in the presence of an excess of hydrogen, passing the reactor eflluent to a'separation zone, separating said effluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the reaction zone to effect a quench of the reactor etlluent prior to its withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase, and recovering the desired product from said liquid hydrocarbon phase.

A further embodiment of this invention is found in a process for the catalytic hydrodealkylation of an alkyl aromatic hydrocarbon which comprises passing said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at a temperature in the range of trom about 1000 to about 1500 F. and at a pressure in the range of from about 300 to about 1000 pounds per square inch, passing the reactor eliluent to a separation zone which is maintained at a pressure of from about 500 to about 600 pounds per square inch, separating said eluent into a hydrogenrich gaseous phase and a liquid hydrocarbon phase containing dealkylated and undealkylated aromatic hydrocarbons, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the reaction zone to effect a quench of the reactor eiuent prior to its withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase recycling a portion of said liquid hydrocarbon phase from said second separation zone to said rst separation zone to admix with said reactor effluent, and recovering the desired product from the remaining portion of said liquid hydrocarbon phase from said second separation zone.

A specific embodiment of this invention is found in a process for the catalytic hydrodealkylation of toluene which comprises passing said toluene to a reaction zone containing a dealkylation catalyst, hydrodealkylating said toluene at a temperature in the range of from about 1000 to about 1500" F. and at a pressure in the range of from about 300 to about 1000 pounds per square inch, passing the reactor eluent to a separation zone which is maintained at a pressure of from about 500 to about 600 pounds per square inch, separating said etiluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase containing a dealkylated and undealkylated toluene, recycling said gaseous phase to combine with said toluene, yrecycling a portion of the liquid hydrocarbon phase to the reaction zone to etfect a quench of the reactor effluent prior to its withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase recycling a portion of said liquid hydrocarbon phase from said second separation zone to said rst separation zone to adrnix with said reactor effluent, and recovering the benzene from the remaining portion of said liquid hydrocarbon phase from said second separation zone.

Other objects and embodiments will be found in the following further detailed description of this invention.

As hereinbefore set forth, this invention is concerned with a process for dealkylating alkyl aromatic hydrocarbons in the presence of hydrogen and a hydrodealkylation catalyst of a type hereinafter set forth in more detail utilizing certain improvements in the process whereby side reactions are minimized and a lesser amount of make-up hydrogen is required. While the principal reaction in the hydrodealkylation of alkyl aromatic hydrocarbons is the elimination of the alkyl groups from the aromatic nucleus, two side reactions may also occur. These side reactions are the decompositionof some of the aromatic nuclei to light paratfins and the condensation `of mononuclear aromatics to poly-nuclear compounds. However, if the process is properly operated, the side reactions are held to a minimum and the ultimate products of aromatic hydrocarbon and light hydrocarbons may be over 90%. lf the feed stock also contains non-aromatic hydrocarbons as well as alkyl aromatic hydrocarbons the former, under the conditions of the process may also be decomposed to light paratiins, principally methane, and therefore the process will produce an aromatic hydrocarbon such as benzene of high purity even though the charge stock contains parains which normally have a boiling range approximately the same as benzene. Along with the controlled temperatures and pressures of the type hereinafter set forth in greater detail, which control the formation of undesired side products, it is necessary to operate the process so as to eliminate the decomposition of methane which is formed during the reaction to free carbon. If this reaction is allowed to occur, massive carbon formation will result and free carbon will be deposited on the walls of the reactor and other pieces of apparatus, in the spaces surrounding the catalyst as well as on the catalyst particles, thereby rendering the catalyst in operative and necessitating frequent shutdowns for decoking of the catalyst or changing the catalyst entirely.

The overall reaction of dealkylation, a specic illustration being the demethylation of toluene to form benzene and methane is believed to involve several free radical steps and is strongly exothermic in nature. While the specific illustration is drawn to the demethylation of toluene to form benzene and methane the process is also eifective in demethylating C8 and higher alkylbenzenes in a successive reaction. Therefore, when utilizing a feed stock containing xylene or higher alkylbenzenes, a greater severity of reaction conditions is required in order to obtain the same molal yield of benzene. Therefore, it is necessary to introduce some means whereby the temperature in the reaction zone is controlled within a predetermined range. If the temperature is allowed to rise into what may be designated as an unsafe range there will be a tendency for the methane to decompose into carbon and hydrogen with the resultant deposit of free carbon in the system. In addition, inasmuch as the process is effected at temperatures in the range of from about 1000 to about 1500 F. or more, certain care must be used in determining what material will be utilized for the reactor, the pipe lines, the heaters, pumps, etc. If the reactor eluent which is discharged 4 from the reaction zone leaves at too high a temperature the pieces of apparatus which are required must therefore, of necessity, consist of high temperature resistant alloys which will raise the cost of the unit whereby the economic operation of said unit will be seriously impaired.

The process of this invention may be effected by contacting an alkyl aromatic feed stock such as toluene, xylene, methylnaphthalene, etc., with an excess of hydrogen in the presence of a dealkylation catalyst at dealkylating conditions, comprising a temperature in the range of from about l000 to about 1500 F. and a pressure in the range of from about 300 to about 1000 p.s.i.g., the feed stock being charged at a liquid hourly space velocity (the volume of feed per volume of catalyst per hour) in a range of from about 0.1 to about 20 and at a preferred range of from about 0.5 to about 5. The reactor effluent is withdrawn from the reaction zone and passed to a high pressure separator which is maintained at a pressure in the range of from about 500 to about 600 p.s.i.g. wherein the effluent is separated into a hydrogen-rich gas fraction and a liquid hydrocarbon fraction. The hydrogenrich gas fraction is recycled to the reaction zone. A major portion of the liquid hydrocarbon fraction is recycledto the reaction zone where it is admixed with the reactor eflluent prior to discharge of said eliuent from the reaction zone thereby effecting the quench of the reactor eluent. The remaining portion of the liquid hydrocarbon fraction may then, if so desired, be charged to an intermediate pressure separator which is maintained at a pressure in the range of from about 50 to about 150 p.s.i.g. Subsequently, the liquid hydrocarbon fraction may be charged to a low pressure separator which is maintained at approximately atmospheric pressure. In the intermediate pressure separator or low pressure separator the light hydrocarbons comprising ethane, methane, etc., are flashed olf and passed to a gas absorber wherein the light hydrocarbons are separated from any aromatic compound or alkyl aromatic compound which may be present and utilized as fuel. A portion of the bottoms from the low pressure separator are recycled back and admixed with the reactor ellluent prior to separation into the gaseous phase in the high pressure separator While another portion of the liquid bottoms are passed to clay treaters for puriiication and thence to fractionators whereby the desired aromatic compounds are separated and recovered, any unreacted alkyl aromatic compound also being recovered and recycled back to form a portion of the feed stock.

By recycling the aforementioned portion of the bottoms from the low pressure separator to admix with the reactor effluent from the reaction zone prior to entry into the aforementioned high pressure separator it is possible to utilize a lesser amount of make-up hydrogen. The hydrogen to ethane and lighter hydrocarbon ratio in the reactor etlluent should be at least 60 mole percent to prevent carbon formation. There are two alternatives to maintain this ratio; (l) suicient make-up hydrogen can be brought into the reactor system to satisfy both the chemical hydrogen consumption and that required to give the aforementioned 60 mole percent hydrogenzhydroearbon ratio in the reactor efuent, or (2) supply a lesser quantity of hydrogen make-up gas and utilize a hydrogen enrichment scheme to increase the utilization of the hydrogen feed gas. It has now been discovered that, as hereinbefore set forth, by utilizing a recycle of a portion of the bottoms from the low pressure llash drum or separator to the reactor effluent will allow a much greater quantity of alkyl aromatic feed with a correspondingly lesser amount of make-up hydrogen. The feed hydrogen utilization for the catalytic hydrodealkylation of alkyl aromatic hydrocarbons can be increased from 35 mole percent (the ratio of chemical hydrogen consumption to make-up hydrogen rate) to mole percent by the use of recycle hereinbefore set forth, thus allowing the process to treat approximately 2.3 times as much alkyl aromatic feed with a given quantity of make-up hydrogen. By utilizing such a recycle step the cost of the operation is greatly decreased inasmuch as less make-up hydrogen is required and thus makes the process more commercially attractive to operate.

The present invention will be further illustrated with reference to the accompanying drawing which is a diagrammatic flow diagram of the preferred embodiment thereof.

Referring now to the drawing which discloses one embodiment of the present invention, a feed which in this embodiment comprises an alkylaromatic hydrocarbon such as toluene is introduced into the system by means of line 1 and passes through heat exchanger 2 through line 3 into heater 4 whereby the feed is heated to the desired operating temperature. The feed then passes through line 5 into reaction zone 6 which may, if so desired, contain a dealkylation catalyst. In the reactor which is maintained at the proper operating conditions of temperature and pressure the dealkylation reaction occur. The reactor etiluent is withdrawn from the bottom of reactor 6 through line 7 where it passes through heat exchanger 2. From heat exchanger 2 the reactor etliuent passes through line 8 to cooler 9 and from cooler 9 through lines 10 and 11 to high pressure separator 12, said high pressure separator or dash drum being maintained at a pressure in the range of from about 500 to about 600 p.s.i.g. The reactor effluent is separated into a hydrogen-rich gaseous phase Which is Withdrawn overhead through line 13 to compressor 14 where it is compressed and passed through line 15 to line 1 where it is admixed with the feed and along with said feed passes through heat exchanger 2 in line 3 to heater 4 and thence back through line 5 to reactor 6. In addition, make-up hydrogen, if so desired, may be admixed with the hydrogen-rich gaseous phase at a point in line 15 by means not shown in the drawing, or may also be admixed with the combined heated feed and hydrogenrich gaseous phase in line 5. The bottoms from high pressure separator or flash drum 12 are withdrawn through line 19, a portion of which then passes through line 20 provided with valve 21 to an intermediate pressure separator 2. Another portion of the liquid hydrocarbon bottoms from high pressure separator 12 passes through pump 23 and line 24 provided With valve 25 Where it joins the feed in line 1. A portion of the liquid hydrocarbon bottoms which is passed through pump 24 and line 24 is recycled to the reactor by means of line 26 provided with valve 27 into the bottom of reactor 6 where it is admixed with the reactor effluent prior to withdrawal of said eiuent from the reaction zone and acts as a quench for the eiiuent thereby lowering the temperature thereof so that said temperature is within a range of from about 1000 to about 140 F. In intermediate pressure separator 22 the light hydrocarbons containing a relatively small amount of aromatic hydrocarbon and alkylaromatic compound are withdrawn as overhead through line 2S while the liquid hydrocarbon bottoms are withdrawn through line 29 provided with valve 30 and passed to a low pressure separator 31. The intermediate pressure separator 22 is maintained at a pressure in the range of from about to about 150 p.s.i.g. while the low pressure separator is maintained at about atmospheric pressure. The light hydrocarbons comprising ethane and methane with a relatively minor amount of aromatic hydrocarbon and alkylaromatic hydrocarbon are withdrawn from low pressure separator 31 through line 32 and compressed in compressor 33. The compressed hydrocarbons are withdrawn through line 34 and commingled with the light hydrocarbons from line 28 and passed to gas absorber 35. In this absorber the gases are contacted countercurrently with absorber oil or glycol and passed through line 36 to be utilized as fuel. The lean absorber oil enters absorber 35 through line 37 and is withdrawn through line 38 where it is passed to a stripper, not shown in the drawing, where the alkylaromatic hydrocarbons and aromatic hydrocarbons are stripped from the oil. The liquid hydrocarbon bottoms from low pressure separator 31 are withdrawn through line 39 provided with pump 40. A portion of the bottoms is recycled through line 41 provided with valve 42 Where it is admixed with the reactor eltluent from reaction zone 6 prior to entry of said eiiluent into high pressure separator 12.

The other portion of the bottoms from the flash drum or low pressure separator 31 which is not recycled to the reactor elliuent passes through line 43, through heat exchanger 44 and from thence through line 45 provided with preheatcr 46 to line 47 provided with valves 48 and 49 to clay treating towers 50 and 51 wherein the effluent is treated to remove any impurities which may be present. From clay treating towers 50 and 51 the purified eiuent passes through line 52 provided with valves 53 and 54 through heat exchanger 44. From heat exchanger 44 the effluent passes through line 55 provided with valve 56 to fractionation zone 57. In fractionation zone 57 the desired aromatic compound is separated from any unreacted alkyl aromatic hydrocarbon and bottoms comprising higher boiling materials which may be present. The overhead from fractionation zone 57 is withdrawn through line 58 provided with condenser 59 to receiving drum 60. The overhead from this receiving drum containing a small portion of light hydrocarbons passes through line 61 back to low pressure separator 31 While the bottoms from the receiving drum passes through line 62 provided with pump 63 and valve 64 back to the fractionation zone. The desired aromatic hydrocarbon such as benzene is withdrawn from the fractionation zone or column through line 65 provided with pump 66, cooler 67 and valve 68 to storage. The bottoms from the fractionation zone are withdrawn through line 69, a portion of which is recycled to the fractionation zone through line 7G provided with heater 7l. The remainder of the bottoms passes through line 69 provided with pump 72 and valve 73 to another fractionation zone or column 76. The overhead from this column is withdrawn through line 77 provided with condenser 78 to receiving drum 79. The overhead from receiving drum 79 is discharged through line 80 While the bottoms pass through line 81 to pump 82. A portion of these bottoms then pass through line 83 provided with valve 84 back to column 86 while another portion is Withdrawn through line 85. A portion of this latter comprising unreacted alkyl aromatic hydrocarbon may be withdrawn to storage through line 86 while another portion passes through line S7 provided with valve 88 and is recycled to line 1 wherein it is admixed with fresh alkyl aromatic feed and passed to the reactor through a means hereinbefore set forth. The bottoms from fractionation 76 are withdrawn through line 89 and provided with pump 90. A portion of these bottoms is recycled to fractionation zone 76 through line 91 provided with heater 92 while another portion passes through cooler 74 and is withdrawn as bottoms through line 93.

Although the drawing has shown the use of three separators or ash drums, i.e., a high pressure separator which is maintained at a pressure in the range of from about 50() to about 600 p.s.i.g., an intermediate pressure separator which is maintained at a pressure in the range of from about 50 to about 150 p.s.i.g. and a low pressure separator which is maintained at approximately atmospheric pressure it is also contemplated within the scope of the invention that only two separators or flash drums may be used. In the event that only two separators are used, one will be maintained at a high pressure in the range hereinbefore set forth while the second one is maintained at approximately atmospheric pressure thus eliminating the necessity for the intermediate pressure separator.

As hereinbefore set forth, the drawing represents one embodiment of the present invention in which an -alkyl aromatic hydrocarbon such -as toluene is hydrodealkylated to form benzene. In another modification of the -present invention an alkyl aromatic hydrocarbon such as methyl naphthalene may be hydrodealkylated to form naphthalene. In the event that the aforesaid methyl naphthalene is used as a feed stock, the flow diagram will undergo some modifications. For example, the reactor elluent is charged to a high pressure separator or flash drum which is maintained at a pressure in the range of from about 500 to 550 pounds per square inch. The hy- -drogen-rich gaseous fraction is withdrawn as overhead and recycled to the reactor while the liquid hydrocarbon fraction is withdrawn and passed through heat exchanger to a stripper. The bottoms from the stripper are withdrawn and charged to a prefractionator wherein the benzene, which may have formed during the hydrodealkylation reaction as a result of the cracking of Some indane which may have been present in the feed stock, is Withdrawn as overhead and recycled to the reactor where it is admixed with the reactor etiiuent, thereby quenching said etlluent. The ybottoms from the prefractionator comprising toluene, xylenes and naphthalene are withdrawn, and the desired products are separated and 4recovered by conventional means well known in the art, while any un- Wanted products formed by side Ireactions or unreacted feed stock may be separated and recycled if so desired.

The catalyst which is utilized in the reaction zone may comprise metal composited on a solid support or carrier, the metal being selected from the platinum group of the Periodic Table; in addition, other metals which may be used include cesium, tungsten, silver, rhenium, and chromium. A particularly preferred catalyst which may be utilized in the present invention comprises chromium composited on a suitable refractory inorganic oxide such as alumina, and more particularly a high surface alumina such as gamma, etaor theta-alumina, said chromia being present in the catalyst in lan amount of approximately to by weight of chromium oxide based on the alumina.

The following example is given to illustrate the process of the present invention which, however, is not intended to limit the generally broad scope of the present invention in strict accordance therewith.

Example 1 In this example a feed containing 197.1 moles of fresh toluene and 1.7 moles of a non-aromatic C7 naphthene is charged to a reactor containing a chroma-alumina catalyst and maintained at a pressure of about 550 p.s.i.g. and an inlet temperature of 1200 F. The fresh feed is combined with 29.6 moles of recycle toluene before entry into said reactor. A ystream of hydrogen containing 1737.8 moles of hydrogen, 893.2 moles of methane, 54.5 moles of ethane, 17.6 moles of benzene and 1.1 moles of toluene is admixed with combined feed. In addition, a makeup hydrogen stream contained `315.7 moles of hydrogen, 19.3 moles of methane, 6.0 moles of ethane and 1.0 moles of propane is admixed with the recycle hydrogen. The toluene undergoes dealkylation in the reactor and the reactor eluent leaves the reaction zone at a temperature of about l350 F. The reactor effluent is passed to a high pressure separator maintained in a range of from about 500 to about 600 p.s.i.g. A hydrogen-rich gas stream is flashed off from this separator and is recycled -to the reactor, said stream containing 1737.8 moles of hydrogen, 893.2 moles of methane, 54.5 moles of ethane, 17.6 moles of benzene and 1.1 moles of toluene. The liquid bottoms from the high pressure -separator are withdrawn, said liquid separator containing 64.4 moles of hydrogen, 217.3 moles of methane, 75.2 moles of ethane, 7158.1 moles of benzene, 1154.1 moles of toluene and 81.9 moles of Cyl- A portion of these bottoms are recycled and divided into two parts, the one portion being admixed with the fresh feed containing 0.1 moles of hydrogen, 0.2 moles of methane, 0.1 moles of ethane, 8.2 moles of benzene, 1.3 moles of toluene and 0.1 moles of C8-|. The other part of this recycle is admixed with the reactor eilluent and acts as a quench, said liquid quench containing 0.9 moles `of hydrogen, 3.0 moles of methane, 1.0 moles of ethane, 100.2 moles of benzene, 16.2 moles of toluene and 1.2 moles of C8l-. The other portion of the liquid hydrocarbon bottoms from the high pressure separator are passed to an intermediate pressure separator which is maintained at a pressure in the range of from about 50 to about 150 p.s.i.g., the net liquid hydrocarbons going to the intermediate pressure separator containing 63.4 moles of hydrogen, 214.1 moles of methane, 74.1 moles of ethane, 7049.7 moles of benzene, 1136.6 moles of toluene and 80.6 moles of high boiling bottoms. The liquid hydrocarbon mixture is ashed in this separator and the gases containing light hydrocarbons are passed overhead to a flash gas absorber, said gas stream containing 55.5 moles of hydrogen, 106.5 moles of methane, 10.1 moles of ethane, 3.10 mole-s of benzene and 0.2 moles of toluene. The liquid hydrocarbon bottoms from this intermediate pressure separator containing 7.9 moles of hydrogen, 107.6 moles of methane, 64.0 moles of ethane, 7046.7 moles of benzene, 1136.4 moles of toluene yand 80.6 moles of high boiling materials are Withdrawn and passed to a low pressure separator which is maintained at atmospheric pressure. In this 10W pressure separator or flash drum the gases are also Withdrawn to the ash gas adsorber, said gas stream containing 7.8 moles of hydrogen, 97.6 moles of methane, 39.5 moles of ethane, 32.5 moles of benzene and 1.8 moles of toluene. The liquid hydrocarbon bottoms are withdrawn from the atmospheric separator, said liquid hydrocarbons containing 0.1 moles of hydrogen, 10.5 moles of methane, 25.9 moles of ethane, 7050.6 moles of benzene, 1136.6 moles of toluene and 80.6 moles of high boiling bottoms. This stream is split into two portions, one portion of the stream containing 0.3 moles of methane, 0.7 moles of ethane, 183.6 moles of benzene, 29.6 moles of toluene and 2.1 moles of high boiling bottoms is passed to clay treating towers, the remainder of the stream containing 0.1 mole of hydrogen, \10.2 moles of methane. 25.2 moles of ethane, 6867.0 moles of benzene, 1107.0 moles of toluene and 78.5 moles of high boiling bottoms being recycled to join the reactor efuent stream prior to entry into said high pressure separator. The flash gases from the intermediate pressure separator and low pressure separator are combined and are passed to a flash gas adsorber wherein the hydrogen and light hydrocarbons comprising 63.3 moles of hydrogen, 203.9 moles of methane vand 48.9 moles of ethane are recovered and utilized as fuel. After passing through the clay treating towers the liquid stream containing 0.3 moles of methane, 10.7 moles of ethane, 183.6 moles of benzene, 29.6 moles of toluene and 2.1 moles of high boiling bottoms are passed to a benzene column fractionator wherein fractional distillation is effected. The gaseous portion of the mixture along with a very small portion of benzene, said Agaseous mixture containing 0.3 moles of methane, 0.7 moles of ethane and 0.9 moles of benzene is recycled back to the low pressure separator which is maintained at atmospheric pressure. A side cut containing 182.7 moles of benzene is withdrawn and passed to storage. The bottoms containing 29.6 moles of toluene and 2.1 moles of high boiling bottoms is passed to a toluene column fractionator wherein the unreacted toluene -is fractionated and recycled to form a portion of the feed stock while the bottoms are withdrawn.

We claim as our invention:

1. A process for the catalytic hydrodealkylati-on of an alkyl aromatic hydrocarbon which comprises passing said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at hydrodealkylating conditions in the presence of an excess of hydrogen, passing the reactor eiluent to a separation zone, separating said effluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the outlet end portion of the reaction zone to eiect a quench of the reactor eiiiuent prior to its Withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase -to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase, and recovering the desired product from said liquid hydrocarbon phase.

2. A process for the catalytic hydrodealkylation of an alkyl .aromatic hydrocarbon which comprises passing said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at a temperature in the range of from about 1000 to about 1500 F. and at a pressure in the range of from `about 300 to about 1000 pounds per square inch, passing the reactor effluent to a separation zone, separating said eflluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the outlet end portion of the reaction zone to effect a quench of the reactor etiluent prior to its Withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase, and recovering the desired product from said liquid hydrocarbon phase.

3. A process for the catalytic hydrodealkylation of an alkyl aromatic hydrocarbon which comprises passing Said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at at temperature in the range of from about 1000 to about 1500 F. and at a pressure in the range of from about 300 to about 1000 pounds per square inch, passing the reactor eluent to a separation zone which is maintained at a pressure of from about 500 to about 600 pounds per square inch, separating ysaid elluent into a hydrogen-rich gaseous phase yand a liquid hydrocarbon phase containing dealkylated and undealkylated aromatic hydrocarbons, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the outlet end portion of the reaction Zone to eiect a quench of the reactor eiuent prior to its withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to `another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase, and recovering the desired product from said liquid hydrocarbon phase.

4. A process for the catalytic hydrodealkylation of an alkyl aromatic hydrocarbon which comprises passing said hydrocarbon to a reaction zone containing a dealkylation catalyst, hydrodealkylating said hydrocarbon at a temperature in the range of from about 1000 to about 1500 F. and at a pressure in the range of from about 300 to about 1000 pounds per square inch, passing the reactor etuent to a separation zone which is maintained at a pressure of from about 500 to about 600 pounds per square inch, separating said eluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase containing dealkylated and undealkylatedaromatic hydrocarbons, recycling said gaseous phase to combine with said alkyl aromatic hydrocarbon, recycling a portion of the liquid hydrocarbon phase to the outlet end portion of the reaction zone to effect a quench of the reactor eiuent prior to its withdrawal from said reaction zone, passing the remaining portion of said liquid hydrocarbon phase to another separation zone, separating light hydrocarbons from said liquid hydrocarbon phase, recycling a portion of said liquid hydrocarbon phase from said second separation zone to said rst separation zone to admix with said reactor effluent, and recovering the desired product from the remaining portion of said liquid hydrocarbon phase from said second separation zone.

5. A process as set forth in claim 4 further characterized in that a major portion of said liquid hydrocarbon phase from the rst separation zone is recycled into said reaction zone.

6. A process as set forth in claim 4 further characterized in that a major portion of said liquid hydrocarbon phase from said second separation zone is recycled to admix With said reactor eiiluent.

7. The process of claim 1 further characterized in that said alkyl aromatic hydrocarbon is toluene.

8. The process of claim 1 further characterized in that said alkyl aromatic hydrocarbon is Xylene.

9. The process of claim 1 further characterized in that said alkyl aromatic hydrocarbon is methylnaphthalene.

References Cited bythe Examiner UNITED STATES PATENTS 2,795,629 6/57 Boedeker 260--672 X 2,795,633 6/ 57 Coonradt et al. 260-672 2,850,436 9/58 Beuther et al 208-355 X ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A PROCESS FOR THE CATALYTIC HYDRODEALKYLATION OF AN ALKYL AROMATIC HYDROCARBON WHICH COMPRISES PASSING SAID HYDROCARBON TO A REACTION ZONE CONTAINING A DEALKYLATION CATALYST, HYDRODEALKYLATING SAID HYDROCARBON AT HYDRODEALKYLATING CONDITIONS IN THE PRESENCE OF AN EXCESS OF HYDROGEN, PASSING THE REACTOR EFFLUENT TO A SEPARATION ZONE, SEPARATING SAID EFFLUENT INTO A HYDROGEN-RICH GASEOUS PHASE AND A LIQUID HYDROCARBON PHASE, RECYCLING SAID GASEOUS PHASE TO COMBINE WITH SAID ALKYL AROMATIC HYDROCARBON, RECYCLING A PORTION OF THE LIQUID HYDROCARBON PHASE TO THE OUTLET END PORTION OF THE REACTION ZONE TO EFFECT A QUENCH OF THE REACTOR EFFLUENT PRIOR TO ITS WITHDRAWAL FROM SAID REACTION ZONE, PASING THE REMAINING PORTIN OF SAID LIQUID HYDROCARBON PHASE TO ANOTHER SEPARATION ZONE, SEPARATING LIGHT HYDRCARBONS FROM SAID LIQUID HYDROCARBON PHASE, AND RECOVERING THE DESIRED PRODUCT FROM SAID LIQUID HYDROCARBON PHASE. 